Method to produce and recover levulinic acid and/or gamma-valerolactone from aqueous solutions using alkylphenols

Abstract

A method to produce levulinic acid (LA) and γ-valerolactone (GVL) from biomass-derived cellulose by selective extraction of LA by alkylphenol (AP) and hydrogenation of LA, in which mineral acid used in the method is recycled and the final concentration of GVL is increased by successive extraction / hydrogenation steps to allow for effective separation by distillation.

Description

FEDERAL FUNDING STATEMENT[0001]This invention was made with government support under W911NF-09-0010 awarded by the ARMY / ARO. The government has certain rights in the invention.BACKGROUND[0002]Significant advances have been made in recent years with respect to using heterogeneous catalysts for converting biomass-derived compounds to fuels and chemicals. Conventional approaches deconstruct solid cellulose into smaller molecules that are soluble in various solvents (e.g., water, ionic liquids), thereby allowing transport of these reactants to the active sites on the heterogeneous catalyst, the majority of which are located within the pores of a high-surface area material. A difficulty in implementing this strategy is that chemical components used to deconstruct solid cellulose (e.g., sulfuric acid) may alter the performance of heterogeneous catalysts used subsequently to convert the soluble biomass-derived reactants to the desired fuels and / or chemicals. As a result, costly purificatio...

AI Technical Summary

Benefits of technology

[0003]Making fuels and chemicals from biomass is complicated by the need to separate and to purify the intermediate platform molecules at high yields. Conventional approaches to making useful chemicals from biomass typically require very difficult and economically unfeasible separation and purification steps. Disclosed herein is a method in which levulinic acid (LA) is first produced from biomass (e.g., corn stover) by cellulose deconstruction. The LA so formed is then extracted from the aqueous phase using one or more alkylphenol (AP) solvents. The LA so formed is a value-added, platform compound that finds commercial use as an intermediate or reactant in a host of industrially useful processes. Additionally, the LA may optionally be hydrogenated to γ-valerolactone (GVL). This strategy allows for any acid that may be used in the process (preferably sulfuric acid) to be recycled very nearly completely (>99%).

[0008]A distinct advantage of the method is that the GVL product is stable during the hydrogenation of LA. Thus, it is possible to increase the GVL concentration in the product mix by successive cycles of cellulose deconstruction, LA extraction, and LA hydrogenation to GVL. By accumulating a large concentration of GVL in the product mix, GVL can be easily (and cost-effectively) separated from the AP solvent by simple distillation.

[0010]Another advantage of this strategy is that the lower degrees of functionality and boiling points of these platform molecules allow for catalytic processing in the vapor phase and / or in organic solvents. This alleviates the need to develop heterogeneous catalysts that are stable under more demanding hydro-thermal reaction conditions. One such platform molecule is levulinic acid (LA) (3, 4) from which a variety of fuels and chemicals can be made, such as valeric acid esters (5), methyltetrahydrofuran (6-8), and esters and ketals of LA (9). Another building block from the reduction of LA is γ-valerolactone (GVL) (10, 11), which can be used directly as a fuel additive (12), or as a precursor for fuels (13) and chemicals (14, 15). While LA can be formed in significant yields (>50%) by cellulose deconstruction in aqueous solutions of mineral acids such as sulfuric acid (SA) (16, 17), a challenge for profitable, large-scale production of LA and its derivatives has been separating the LA from the mineral acid used in the process. This is necessary so that the LA can be further processed downstream without the negative effects of the mineral acid (18).

[0011]In the present method, alkylphenol (AP) solvents (19) are used as a partitioning agent in a method to produce LA and / or GVL from biomass in general, and lignocellulosic biomass in particular. As illustrated schematically in FIG. 1, AP solvents can be used to selectively extract LA from aqueous solutions after a cellulose deconstruction step. In addition, AP solvents extract GVL from water with a higher partition coefficient (the concentration of the solute in the organic phase divided by the concentration of the solute in the aqueous phase) compared to LA. Accordingly, the GVL concentration in the AP solvent can be increased by the conversion of LA to GVL, combined with the recycle of this stream for successive extractions. Importantly, a preferred carbon-supported RuSn catalyst (20, 21) can be used to selectively reduce LA to GVL by hydrogenation in the presence of AP, without hydrogenation of the solvent. This is a critical discovery in that it enables the aforementioned recycling strategy for enhancing the GVL concentration. This then enables the easy and cost-efficient recovery of the GVL from the AP solvent by simple distillation. After distillation of GVL from the organic phase, the aqueous phase containing any residual LA and possibly acid (after extraction with the AP solvent) can be recycled for subsequent cycles of cellulose deconstruction, providing an effective strategy for managing the acid used in the deconstruction of the incoming biomass.

[0013]APs do not partition water or mineral acids. Thus, if an aqueous acid solution is used to deconstruct the incoming cellulose, it may be recovered entirely and recycled accordingly. The relatively high boiling point of APs allows LA and / or GVL to be distilled from the organic phase without vaporizing water. The APs are organic solvents that are inert under many upgrading reactions, such as selective hydrogenation. Because the APs have very high partition coefficients for GVL, the GVL can remain in the organic phase when LA is extracted from an aqueous solution. This allows the GVL concentration in the product stream to be increased by recycling the product stream for additional cycles of LA extraction from the aqueous phase containing LA. GVL also increases the extraction of formic acid from the aqueous reaction solution.

[0014]Another advantage is that the ultimate products (either LA or GVL) can be recovered by distillation without having to evaporate water—only the product itself is evaporated. The AP solvent does not require any further evaporation or separation, and can be directly recycled for additional extractions. Likewise the aqueous reaction solution used to deconstruct the incoming biomass can also be recycled without further purification. This solution may contain homogeneous acid catalysts, which are recovered intact after extraction.

Problems solved by technology

Making fuels and chemicals from biomass is complicated by the need to separate and to purify the intermediate platform molecules at high yields.

Conventional approaches to making useful chemicals from biomass typically require very difficult and economically unfeasible separation and purification steps.

Images